Metering (Measuring light) A beginners guide

Most digital cameras have an exposure meter that is visible when looking through the viewfinder. The exposure meter is usually represented by a bar or dots with a pointer. Take a look at your camera’s manual to see how it is displayed on your specific model.

The meter tells us how much light is in the scene (image) we want to take so that we can set the ISO, Aperture and shutter speed for a correct exposure (not too dark or too light).
Using ‘Manual’ mode, if we decide we want our image to be darker we can adjust our settings so that the meter is to the negative side of the meter. For a lighter image we would want the meter on the positive side.

There are three main ways or ‘modes’ a DSLR camera meters (measures) the light in our image.
•    Centre-Weighted. 
•    Evaluative.
•    Spot.
Each of these modes assigns a different weight to a portion of the image for metering. Basically the camera will take more notice of the white areas shown in the diagrams below when measuring the amount of light in our composition. 

Centre weighted and Spot metering give us more control over our metering than Evaluative. However, this means a little more work on our part to get the image we want.

Centre-Weighted metering
In general, Centre Weighted metering is used more often than most. As an example, imagine we want to take an image of a subject where a light source is behind them; this could be the Sun, a light sky or even a light we have placed behind them. We want to meter (measure the light) on the subject more than the background so that the subject is correctly exposed. 

In this example image using Centre Weighted metering the camera is measuring the area shown below ignoring most, but not all of, the surrounding area.  This allows us to expose for our subject more than the background.

Spot Metering
Although Spot metering could equally be used in the example above, it is in general used less than Centre Weighted as the metering area is quite small. This can be of advantage if you wish to meter a smaller object or specific point within your image, for example a grey card. We’ll talk more about grey cards in another 'Hints & Tips' when we'll talk about White Balance (WB).

Evaluative Metering
This used to be the default metering setting in most DSLR cameras. Evaluative metering copes very well with bright sky and dark landscapes and is highly recommended for beginners in landscape photography. It meters light across the whole image.

Post by Mark